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Silent Generators: Do Gensets Have to Be Noisy?

A genset, whether diesel or petrol, can produce a high level of noise that can be particularly intrusive and irritating to humans and animals. Noise, which is measured in decibels, can adversely affect human health and regulations exist to limit the amount of noise that is permissible in certain areas. If one is forced to live or work in close proximity to a noisy genset for extended periods, permanent damage to your hearing may occur. With the current unreliability of our grid power supply, we have all experienced the buzz and drone of a multitude of small gensets starting up in our suburbs when the grid goes down. To keep the costs down, small petrol-powered gensets almost never come equipped with any form of noise attenuation.

If you have a neighbour who uses one of these small gensets during load shedding or technical outages, you will be painfully aware of just how much of a nuisance the noise they produce can be. Genset noise is measured in A-weighted decibels [dB(A)], with the “A” indicating that only frequencies audible to humans are taken into account. Genset manufactures will give their gensets a dB(A) rating. The more powerful the genset is, the noisier it will be and the more it will require some form of noise control. For this reason, many residential estates do not permit the use of gensets by their homeowners.

As noisy and annoying as the small units can be, they produce a fraction of the noise that their large industrial and commercial diesel-powered counterparts do. For this reason, unless a commercial or industrial genset is to be installed far from where people work or live, something has to be done to reduce the noise. Silent generators were created to attenuate the noise which is primarily produced by the diesel engine powering the genset. While the manufacturers of engines for gensets do as much as they can in the design of their engines (most of their efforts are centred on the exhaust design), to make them as quiet as possible, there is only so much that they can do. To make diesel gensets that qualify as silent generators, the entire genset is housed and runs inside a specially soundproofed container or enclosure.

The enclosures are specifically designed and engineered to deaden the noise produced by large diesel engines. These enclosures are referred to as sound-attenuating enclosures. Enclosures for silent generators are typically made from steel, aluminium, or a composite such GRP (glass-reinforced plastic). A combination of approaches is used in the manufacture of enclosures for silent generators. A layer of hard, reflecting material is employed to bounce the sound energy back into the enclosure, combined with layers of soft, sound-absorbent materials designed to absorb the sound energy. Sound energy is then converted into heat and dissipated into the atmosphere.

The hard reflective layer is usually a single skin while different types of soft, porous materials are layered to absorb a spectrum of sound frequencies in the higher frequency range. Lower-frequency sound produced by a genset is harder to mitigate. The best results for damping lower-frequency sound comes from the use of trapped pockets of air which convert the low-frequency sound via resonance to a higher pitch, which is easier to deal with. Silent generators use combinations of several layers of materials in their enclosures to reduce noise as far as possible and obtain the best decibel ratings. Silent generators are typically mounted on rubber, isolation, feet, or rubber mats to reduce the noise produced by the transfer of vibrations to the surface on which the genset is mounted.

How Quiet Are They?

 Gensets range from open skid units (no enclosure) to units known as “whisper units”. All silent generators will have some form of enclosure (also known as an acoustic canopy), without which noise reduction is virtually impossible. Although the word “silent” is used for generators with an acoustic canopy, silent generators are by no means absolutely silent. A spectrum of silent generators, with different decibel ratings, is available. Generally, the quieter the unit needs to be, the more expensive it will become. Producing really silent generators requires sophisticated engineering and more exotic materials. To produce a genset with a very low decibel rating is consequently considerably more costly than it is to produce an open skid model.

Generally, to be considered silent generators, units need to fall into a range from 75 to 85 dB(A) at one meter distance. To provide some perspective, the dB(A) rating of normal conversation is around 65 dB(A) while the sound of a petrol-powered lawnmower would be around 90 dB(A). Bear in mind that decibel measurement is not linear but logarithmic – in other words, for each increase of 10 decibels, the noise level doubles. Most people will experience pain and discomfort at sound levels of 140 decibels or higher and continued exposure at this level will cause permanent damage to their hearing.

The Advantages of Silent Generators

Silent generators can be situated in areas where environmental noise levels are stringently controlled or set to maximum levels by regulation. Silent generators are suitable for sites such as high-density residential areas, shopping malls, hotels, and other places with strict limits on environmental noise. Even tough they are significantly more costly, very low decibel units, the so-called “whisper” gensets may be employed where noise reduction is absolutely critical. Examples of applications where ”whisper” units are used include backup power at medical facilities and primary power or on location television and film sets.

Choosing The Best Supplier

PacB is renowned in the industry as a manufacturer of superior-quality large silent generators. The larger the genset, the more noise it produces. Our team specialises in large industrial and commercial gensets. If your requirement is for silent generators, we at PacB have years of experience building silent generators to exacting technical requirements. Expertise includes not only noise attenuation, but also knowledge on generator sizing, fuel type, and system configuration and integration. We can assist with the design and manufacture of any generator of any size, as well as providing the correct control systems, including various AMF (Automatic Mains Failure) and ATS (Automatic Transfer Switch) systems and all the additional components for even the most complex and technically demanding installations.

We are able to design and manufacture Synchronous PLC controlled panels for multi-station generator supply over a vast range system of sizes and voltages, including systems in excess of 1000 kVA. With the continuity of supply issues South Africans are currently experiencing as Eskom struggles to supply power reliably, a backup genset is becoming mandatory for most commercial and industrial entities. Contact PacB today!